The present invention relates to a fuel injection valve.
In U.S. Pat. No. 5,299,776 is discussed a fuel injection valve that has a valve closing member that is connected to a valve needle and interacts with a valve seat surface provided on a valve seat body to form a sealed seat. A magnetic coil, which interacts with an armature that moves on the valve needle between a first stop limiting the armature movement in the lifting direction of the valve needle and a second stop limiting the armature movement against the lifting direction, is provided for the electromagnetic operation of the fuel injection valve. Within certain limits, the axial armature clearance defined between the two stops isolates the inert mass of the valve needle and the valve closing member and the inert mass of the armature. This counteracts a rebounding of the valve closing member from the valve closing surface within certain limits when the fuel injection valve closes. It is believed that bounce pulses of the valve needle and valve closing member, respectively, cause the fuel injection valve to open briefly in an uncontrolled manner, making it impossible or impractical to reproduce the metered amount of fuel and resulting in an uncontrolled injection. However, since the axial position of the armature in relation to the valve needle is completely undefined due to the free movement of the armature in relation to the valve needle, bounce pulses can be avoided only to a limited extent. Accordingly, it is believed that it is not possible or practical to prevent the armature from striking the stop facing the valve closing member while the fuel injection valve closes, abruptly transmitting its pulse to the valve needle and thus also to the valve closing member. This abrupt pulse transfer can produce additional bounce pulses of the valve closing member.
In U.S. Pat. No. 4,766,405 is discussed a method for dampening the force of the armature striking the stop facing the valve closing member. In particular, a damping member made of an elastomeric material, such as rubber, is placed between the armature and the stop. However, it is believed that, elastomeric materials have the disadvantage that their damping performance depend on temperature, and the damping effect decreases as the temperature rises. In addition, it is believed that elastomeric materials have a limited long-term stability, particularly when they come into contact with the fuel injected by the fuel injection valve. Elastomeric material aging can limit the service life of the fuel injection valve. Mounting a damping plate made of an elastomeric material may be is complicated. Vulcanizing the elastomeric material onto the armature or stop maybe equally complicated. In addition, it is not believed to be possible or practical to selectively adjust the damping characteristics.
The provision of a damping spring in the form of a cup spring between the valve seat body and a valve seat carrier, on which the valve seat body is mounted, thereby causing the valve closing member to come to rest gently against the valve seat surface provided on the valve seat body, is discussed in U.S. Pat. No. 5,236,173. It is believed however, that this damping method has the disadvantage that the valve seat body swings back in the direction of injection after the valve closing member comes to a stop, while the valve closing member either remains stationary or even moves away from the valve seat body against the direction of injection as a result of pulse reversal. Valve bounce pulses can therefore occur with even greater intensity in this fuel injection valve design, which is why this damping method may not have widely accepted.
The fuel injection valve according to an exemplary embodiment of the present invention is believed to have on advantage over the related art since the fuel injection valve is satisfactorily debounced. It is also believed to have a high long-term stability, since the damping spring has a longer service life than does an elastomeric material and, in particular, does not disintegrate over time when exposed to fuel. Compared to an elastomeric material, the damping spring is also relatively easy to install, and the damping effect is not dependent on temperature. It is also possible to selectively adjust the damping characteristics by selecting a suitable material and shape for the damping spring as well as the setting angle of the damping spring in relation to the stop and the armature, and choosing the damping spring pretension.
The fuel located in the gap between the armature and the stop flows in a compressed stream between the armature and the stop. This compressed flow results in further damping.
The damping spring may be a cup spring that surrounds the valve needle in the shape of a ring. The cup spring forms a compact damping component that can be integrated into the gap between the armature and the stop. The cup spring is also extremely easy to install; it only needs to be pushed onto the valve needle before mounting the armature.
The stop is advantageously convex, while the opposite end face of the armature can be designed with a correspondingly concave shape or, conversely, the stop can have a concave shape and the opposite end face of the armature a convex shape. This causes the gap between the armature and the stop to slope toward the longitudinal axis of the valve needle, improving the damping action through the compressed fuel flow. In addition, a cup spring having a flat spring washer, which is easy and economical to produce, can be used if the stop and opposite end face of the armature are designed with a convex and concave shape, respectively. In addition to the flat spring washer, the cup spring can also have a conical or domed spring washer, thus improving the damping effect even further.
Alternatively, it is possible to give the stop and opposite end face of the armature a flat design, in which case a cup spring with a conical or domed spring washer is used. It is even possible to use two conical or domed spring washers that are arranged consecutively in the axial direction so that either their convex sides or their concave sides are facing one another. The two spring washers can be interconnected by a connecting strap, making them easier to mount. The two spring washers can also be produced, for example, by punching them from a continuous strip of sheet metal.
To adjust the damping characteristics of the cup spring, the spring washers can have openings that influence the spring rigidity of the spring washers and also affect the compressed flow of fuel in the gap between the armature and the stop.
A further damping spring can be provided between the stop limiting the movement of the armature in the lifting direction and the armature to prevent the armature from striking this stop too forcefully and producing valve bounce pulses.